Microscopic Behavior And Properties Of CFRP Interface Under Electrothermal Loading

Carbon fiber reinforced polymers(CFRP)are widely used in civil aircraft structures and are subject to complex environments during service,while low-intensity currents have less concern for CFRP.The research goal of this paper is to obtain the interface temperature of carbon fiber/epoxy composite under weak-current,and obtain the evolution law of the carbon fiber/epoxy interface shear strength and the compression properties after impact(CAI)of the laminate structure under electro-thermal effect.Through analyze the interfacial stress and interfacial physicochemical properties under electro-thermal effect,reveals the evolution mechanism of carbon fiber/epoxy composite performance.The main research contents and results are as follows:The interfacial phase size of carbon fiber/resin composites is very small,the interface temperature under electro-thermal cannot be directly obtained.In this paper,the interface temperature of carbon fiber/resin composite is indirectly obtained by using the temperature-sensitive properties of carbon fiber.When the loading current of monofilament carbon fiber is 0~8mA,the interface temperature varies from 25 to 225°C.The results of monofilament fracture test show that the interfacial shear strength of carbon fiber monofilament/epoxy composite samples increases first and then decreases.The inflection point current intensity is 6mA,the interface temperature reaches 140°C,and the shear strength of the interface increase to 62.39(±1.02)MPa,which is 22.50%higher than the untreated sample.The evolution law of carbon fiber/resin interfacial stress under electro-thermal effect is measured by the change of G'peak of Raman spectroscopy.When the current is 3mA,the interface temperature reaches 65°C,the interfacial compressive stress changes from monotonic increase to monotonic decrease.When the current exceeds 6mA,the interface temperature exceeds 140°C,the G'peak of carbon fiber disappears.In addition,the results of DSC experiments show that the T_g of the carbon fiber/resin interface increases from 80.12°C to 128.54°C at 0~6mA,and T_g begins to decrease when it exceeds 6 mA,and drops to116.78°C at 8mA.The experimental results of IR and XPS reveal the main mechanism of carbon fiber/resin properties,interfacial stress and Tg after electricity.The content of epoxy group and ether bond of carbon fiber/resin changed obviously under loading current.When the current is low,as the current intensity increases,the epoxy group and ether bond content increase,so the stress,T_g and bonding strength of interface are all improved.But when the current intensity reaches 6mA,the interface temperature exceeds 140?,the fatty ether group in the macromolecular chain of interface component is broken,the crosslinked structure of the polymer is broken down,the G'peak of carbon fiber disappears,so the T_g and bonding strength of interface component both decreased.The carbon fiber/epoxy laminate sample heating-up rapidly under the effect of current,and reach the steady temperature at about 200s.The steady temperature of the sample increases with the increase of current intensity and exceeds 200°C at 35A.The results of impact and CAI experiments show that the impact resistance and the CAI performance of the laminate under electro-thermal reduce slightly and then reduce greatly.The CAI intensity changes from 202.17MPa to 203.96MPa at 0~20A,begins to decrease when the current exceeds 20A,and drops to 146.60MPa at 40A.